Read stlink version info via libusb.

Hooray! Stage 1 complete.  The stlink version can now be read by sending the scsi
commands via libusb directly, instead of using sg-utils.  It's very very prototype code
however, but should come together from here.

Major bugs: Only works when the device has been first plugged in.  I'm clearly not
resetting some usb state somewhere.

Now that libusb is being used directly, you can use linux usb-storage quirks to
completely IGNORE the device as mass storage.  We'll just grab it via libusb when we
want it.